Creative Product Project

Research on different types of Sundial:

1. Vertical sundials

Vertical dials are commonly mounted on the walls of buildings, such as town-halls, cupolas and church-towers, where they are easy to see from far away. In some cases, vertical dials are placed on all four sides of a rectangular tower, providing the time throughout the day. The face may be painted on the wall, or displayed in inlaid stone; the gnomon is often a single metal bar, or a tripod of metal bars for rigidity. If the wall of the building faces toward the South, but does not face due South, the gnomon will not lie along the noon line, and the hour lines must be corrected. Since the gnomon’s style must be parallel to the Earth’s axis, it always “points” true North and its angle with the horizontal will equal the sundial’s geographical latitude; on a direct south dial, its angle with the vertical face of the dial will equal the colatitude, or 90° minus the latitude.

Houghton_Hall_Norfolk_UK_4-face_sundial

2.Equatorial sundials

The distinguishing characteristic of the equatorial dial (also called the equinoctial dial) is the planar surface that receives the shadow, which is exactly perpendicular to the gnomon’s style. This plane is called equatorial, because it is parallel to the equator of the Earth and of the celestial sphere. If the gnomon is fixed and aligned with the Earth’s rotational axis, the sun’s apparent rotation about the Earth casts a uniformly rotating sheet of shadow from the gnomon; this produces a uniformly rotating line of shadow on the equatorial plane.

2007122712957338_2

3.Vertical sundials

In the horizontal sundial (also called a garden sundial), the plane that receives the shadow is aligned horizontally, rather than being perpendicular to the style as in the equatorial dial.

sundial_horiz_r1

http://en.wikipedia.org/wiki/Sundial

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